1. Field of the Invention
This invention relates to a method and apparatus for separating magnetisable particles from a fluid in which they are suspended.
2. Description of the Prior Art
It is known from U.S. Pat. No. 2,452,220 in the name of William Leslie Bower to separate ferrous metal particles from a fluid, particularly a liquid such as lubricating oil, by passing the fluid containing the metal particles through a separating chamber containing a plurality of magnetisable balls forming a regular and uniformly arranged system of interstices therebetween, whilst a magnetic field is applied within the separating chamber by means of a permanent magnet. The ferrous particles within the fluid are thereby magnetised and attracted to the magnetisable balls. To remove the ferromagnetic particles attracted to the magnetisable balls from the separating chamber, the permanent magnet may be removed from the vicinity of the separating chamber so that the magnetisable balls are demagnetised and a fluid may be flushed through the separating chamber.
It is also known from U.S. Pat. No. 3,567,026 in the name of Henry H. Kolm to separate magnetisable particles from a fluid by passing the fluid through a substantial volume of ferromagnetic corrosion resistant wool material around which an electromagnet coil, capable of applying a magnetic field to the material of at least 12,000 gauss, is wound. When this field is applied, the magnetisable particles in the fluid are attracted to the material in a similar manner as in the previously described process. To remove the magnetisable particles from the material, the magnetic field is turned off and the material is flushed by a fluid whilst being vibrated by means of an applied A.C. magnetic field.
Furthermore, it has hitherto been usual in magnetic separation apparatus, in which an electromagnetic coil is used to establish a magnetic field in a separating chamber containing a porous packing of magnetisable material, to keep running costs down, while maintaining a high magnetic field in the separating chamber, by providing a massive iron return frame, weighing tens or even hundreds of tons, to minimise the loss of magnetic flux from the region of the separating chamber, and thereby minimise the operating power required to maintain a given high magnetic field.
U.S. Pat. No. 3,627,678 describes such an apparatus, in which the return frame almost completely surrounds the separating chamber. It is not possible to remove the separating chamber from between the pole pieces of the electromagnet coil without first removing a massive iron top member of the return frame.
In order to remove magnetisable particles trapped in the material within the separating chamber, it is necessary to flush out the separating chamber in situ; and the electromagnet coil must, of course, be de-energised before the more strongly magnetisable particles are released from the packing material. This is disadvantageous, since while the coil is de-energised, no magnetic separation can take place. A high proportion of time for which such apparatus is in operation is therefore spent cleaning out the packing material, that is in carrying out a strictly non-productive process.
U.S. Pat. No. 3,627,678 also discloses that the electromagnet coil may operate superconductively and that, in this way, running costs may be reduced, since the reduction in electric power needed to maintain a given field strength which occurs when a superconductive magnet is utilised more than compensates for the power required to refrigerate the magnet coil. However, it is not economic to repeatedly energise and de-energise a superconductive magnet coil.